Oxidative demethylation of lignin



3,971,570 Patented Jan. 1, 1983 This invention relates to alkali ligninderivatives possessing increased aromatic reactivity and relatesparticularly to a process for treating lignin recovered from spentalkaline cooking liquors whereby increased aromatic reactivity isimparted thereto.

Lignin, as it occurs in wood, has been extensively investigated inrecent years to determine its botanical origin and chemical structure.Lignin has usually been considered to be composed of structural elementssuch as phenyl and furan groups with an assortment of hydroxyl andmethoxyl groups, but, according to modern views on the structure oflignin as it occurs in coniferous woods, this natural product is builtup of guaiacyl propane units which are linked together with differenttypes of bonds, in some 2O propane unit and which are Typical compoundswhich incorporate the guaiacylbelieved to be proper models for buildingstones of softwood lignins, with probable types of linkages illustrated,are:

l O Qll ofi a? 3 'sa H4 k C F o Ju gi tsgaugasg u, E 552F1 HG CH 5 1 H-co 3 case "a l Seli W i i 06H i L" new I R Hydrogen atom or carbon -a oomof another guaiacyl propane chain.

the carbon atoms of the propyl It is widely acknowledged, however, thatsulfate cooking, in particular, substantially increases the proportion,in softwood lignin, of guaiacyl propane building units having a freephenolic group in the No. 4 position as compared to natural lignin;breakage of aryl-alkyl-ether bonds by thioalcohol groups in alkalinesolution is thought to be responsible. Since the structure of lignin,particularly the altered lignin recovered after alkaline digestion ofwood, is not known with precision, the reactions which occur cannot bestated with exactness, but it is believed that certain reactions takeplace, as deduced from studies of model compounds, which are reasonablyconsonant with those set forth hereinafter.

As is well known, the presence of a free phenolic hydroxyl increases thearomatic reactivity of both of the adjacent (ortho) positions and of theopposite (para) position on an aromatic nucleus. Since the para positionof a guaiacyl propane unit (position No. l) is usually occupied by thepropyl chain and one of the ortho positions (position No. 3) is filledwith a methoxyl group, the only remaining position possessing potentialaromatic reactivity is the other ortho position, hereinafter termed theNo. 5 position, which may or may not be filled by a linkage with apropyl carbon of another guaiacyl propane unit or even by a diphenyltype of bond. Disregarding the relatively small proportions ofaldehydic, ketonic, and alcoholic groups on the propane side chains,which are non-aromatic in their reaction conditions, the principaldeterminative factor in the reactivity of natural lignin is the numberof these No. 5 positions-on the guaiacylic nuclei which are unoccupied.Similar considerations are valid for hardwood lignin, except thatsyringyl groups occur in addition to guaiacyl groups.

If the compounds incorporating guaiacyl propane units, as describedhereinbefore, represent those which have persisted in softwood ligninthrough alkaline digestion and recovery processes, it is clear that bothfree and condensed S-positions may exist on the aromatic nuclei of thephenolic guaiacyl propane units. Replacement of methoxyl groups (inposition No. 3) with hydroxyl groups, moreover, should add twoaromatically reactive positions (one ortho and one para, positions 2 and6) to each aromatic ring having a condensed S-position, therebymultiplying significantly the total aromatic reactivity of the recoveredlignin and enhancing its usefulness in many applications.

For example, in the case of guaiacyl-propane units having a free5-position, there would be two new reactive positions created ortho andpara to the new phenolic OH group, as in the trifunctional demethylationproduct on the right below, where the reactive positions are marked withan asterisk:

ocH H For guaiacyl-propane units containing condensed and therebyblocked 5-positions, the demethylation product becomes bifunctional:

Chemical building units of trifunctional or bifunctional nature,containing guaiacyl propane units converted into pyrocatecholstructures, should show considerably increased reactivity towardsformaldehyde and greater cross-linking potential in many usefulreactions.

Among studies of model compounds of the type believed to occur in ligninhave been several studies on the aromatic substituents of guaicol andguaicol-based deriva- A tives. For instance, Adler desc bed in ActaChemica Scandanavia 9 (1955), No. 2, 319-334, an analytical method fordetermination of guaiacyl groups which depended upon sodiummetaperiodate liberating methanol quantitively by a rapid oxidativedemethylation process from guaiacol and similar compounds but not fromcompounds of the veratrol type in which the phenolic group in the No. 4position had been etherified, forming an additional methoxyl group or alinkage with a carbon of an adjacent compound.

In these determinations the periodate solution was allowed to react at 4C. upon the model compounds or the protolignins for as long as hours. Toobtain substantially complete demethylation, a reaction time of 16 to 48hours was necessary. The reactions were stopped and the compounds wereprecipitated by addition of a solution of lead nitrate.

Experiments with natural lignins, reported in Svensk Papperstidning, 61(1958), 18B, 641-647, showed that these materials also produced methanolupon treatment with sodium metaperiodate, leaving highly polymerized,unreactive lignin residues which were generally insoluble in the usuallignin solvents. In contrast to the rapid production of methanol byguaiacol-type compounds, however, these lignins liberated methanolpartially in a rapid phase and partially in a slow phase.

Somewhat similar to the oxidative demethylation process forming aportion of this invention is the reductive dimethylation process withhydriodic acid, as given by Moore et al., in the Canadian Journal ofResearch, 15B (1957), page 532, in which high reaction temperatures, ahigh concentration of H1, an excess of HI, and a lengthy reaction timeare required. Reductive demethylation, moreover, is not specific as isoxidative demethylation, for many methoxyl types, including bothguaiacyl and veratryl, are attacked, and the reductively demethylatedlignin product is polymerized and destructively degraded to a non-usefulproduct.

One of the most widely-available sources of lignin is spent liquor inthe sulfate and soda processes which is commonly concentrated and burnedto recover heat values and inorganic cooking chemicals. This lignin maybe recovered as a water-soluble alkali lignate or as a waterinsolublealkali lignin of low ash content by processing the concentrated, spentcooking liquor according to the principles and methods of US. Patent No.2,464,828. It must be borne in mind, however, that after undergoing therelatively drastic conditions occurring in the digestion of wood by thesoda or sulfate processes, the natural lignin in either hardwoods orsoftwoods is changed to a degree that is unknown and as yet onlycursorily investigated.

In studies of alkali lignin recovered from spent sulfate liquor afterdigestion of coniferous woods, it has been determined that, of theguaiacyl propane units which are believed to comprise the lignin, nearlytwo-thirds are phenolic in type, having free phenolic OH groups inposition No. 4. Of these phenolic guaiacyl propane building units, aboutone-third possess a position ortho to the phenolic hydroxy (i.e., theNo. 5 position on the phenyl ring) which is free and thus accessible tothe introduction of methylol groups, for instance, by aromaticreactions. Using very approximate averages, out of every guaiacylpropane building units, therefore, about 22 are phenolic groups andpossess free No. 5 positions with resultant capacity to becometri-functional after demethylation, about 42 are phenolic groups andpossess blocked No. 5 positions with resultant capacity to becomebi-functional after demethylation, and about 36 are non-phenolic groupshaving etherified No. 4 positions which are apparently incapable ofaromatic reactivity or of attaining increased aromatic; reactivity bythe methods of this invention.

Chemical determination of hydroxyl groups was made. according to themethod given in Chemische Berichte, 88, 617 (1955) in an article by K.Freudenberg and H,

j H+ was,

Alkali lignin, recovered according to US. Patent No. 2,464,828, has beenutilized as an extender of phenolformaldehyde resins, urea-formaldehyderesins, epoxy resins, isocyanate foams, and styrene-butadieneelastomers. A method of increasing the aromatic reactivity of thislignin has wide usefulness in many practical applications, involvingsuch fields of use as casting sands, paper and fiberglass laminates,wood glues, hardboard, molded articles, insulation foams leathertanning, rubber tires, and rubber heels.

The object of this invention is to increase the reactivity of alkalilignin and more specifically to increase the reactivity of alkali lignintoward aldehydes.

A chemically sound way to attain this objective is to increase thearomatic reactivity of the lignin whereby additional substitutionreactions on the guaiacol nucleus may be used for accomplishing suchreactions as chloromethylation, the Mannich reaction,phenol-formaldehyde resin condensations, urea-furfural resincondensations, bromination, and nitration, for example. Conversion ofguaiacyl structures in softwood-derived alkali lignin into pyrocatecholstructures and of syringyl structures in hardwood-derived alkali lignininto pyrogallol structures by replacement of methoxyl groups withhydroxyl groups is a practical way of attaining increased aromaticreactivity.

It has now surprisingly been found that the periodate reaction can beutilized to increse the aromatic reactivity of alkali lignin bycarefully controlling the extent of oxidative demethylation and rapidlyreducing the product obtained thereby.

Increased aromatic reactivity in alkali lignin is attained according tothis invention by dissolving the lignin in a solvent that is inert tothe oxidative demethylating agent, adding and rapidly mixing theoxidative demethylating agent, and quickly stopping the reaction with areductant, the degree of reaction being controlled by removing heat fromthe reaction materials before mixing or during the reaction and bylimiting the duration of the reaction.

It is believed that this invention is effective because the oxidativedemethylation reaction of sodium metaperiodate upon alkali lignin doesnot convert methoxyl groups to hydroxyl groups but instead forms quinonegroups which are veryreactive and tend to dimerize by diene-addition andform a lignin product of lowered reactivity and insolubility:

example, is usable, but ethanolarnine is not.

Therefore, by adding an excess of a reductant such as sulfur dioxide toremove any excess of the demethylating agent and to convert thedemethylated lignin into a somewhat less reactive form, polymerizationby diene-addition can be avoided and a stable lignin product ofincreased aromatic reactivity can be obtained.

The reaction which seems to occur in the oxidative demethylationprocedure may be expressed, for a typical guaiacol-propane unit,employing sulfur dioxide as the reductant source, as:

Other oxidants are able to oxidatively demethylate lignin. For instance,the lithium, sodium and potassium salts of bismuthate, persulfate,tungstenate, chlorite, hypochlorite, hypobromite, and hypoiodide anionsand chlorine dioxide with chlorine are effective agents. Hydrogenperoxide and ozone are also potentially useful oxidative demethylants.For reduction, a choice might be made among sulfur dioxide and lithium,sodium, and potassium thiosulfate.

The oxidative demethylation reaction may be conducted in any ligninsolvent which is itself compatible with periodic acid, for the periodateion, as liberated by the acid or any of its salts, is actually theactive agent in this reaction. The reaction, moreover, is catalyzed byprotons, and for this reason a-lkalis are not usable. Phenol, for

Suitable solvents, for example, are acetic and formic acids and theirchlorinated derivatives, 1,4-dioxane, dimethyl sulfoxide, ethylenechlorohydrin, thymol, and the cresols. If an organic solvent isselected, however, it is necessary to add an aqueous acid for theoxidative demethylation step; it is also desirable to have at least twomoles of water for each S0 mole present during the reduction step as asupply source for hydrogen ions.

Experimental work was performed on purified alkali lignin isolated fromspent sulfate liquor after digestion of southern pines in a typicalkraft papermakiug process. The experimental results, as to yield andmethoxyl contents of the oxidized and 'SO -reduced products, are givenin Table 1. The experimental procedure in general which was used isillustrated hereinafter by Example No. 8 in which the reaction wasconducted at ice-water temperatures.

EXAMPLES 1-7 In Examples 1, 2, and 3, 1.85 ocH -rnilliequivalents ofalkali-pine lignin (0.4 g.) were dissolved in 2.5 ml. of warm aceticacid; after cooling to 20 C., 30 m1. of a 0.14

worked up as described in Example AcOH, and 250 ml. of 0.14

molar NaIO solution were used (reaction time 20 min.). After reductionwith S fractional dilution with water yielded a first precipitate (4a)in 58% yield, and a further one (4b) in 9% yield. Similar yields wereobtained in Examples 1-3 for the initial precipitation only. Example .5was run in a non-solvent acid medium, 0.14 molar H SO at 20 C. for 30minutes, tent was merely reduced to 13.72%.

Examples 6 and 7 were made with sodium persulfate, Na S O as the sole orprincipal oxidative agent, but the resulting reduction in methoxylcontent was inconsequential. It was concluded that lignin would not bedemethylated to an effective degree if reacted upon when in slurry form.

Table 1 but the methoxyl con-.

and SO -reduction must have been phenolic hydroxyl groups, available forremethylation by diazomethane, and that only a minor amount of theintermediate o-quinoid groups could have undergone dimerization.

The same secondary periodate precipitate in 12% yield (817) was reducedwith sodium borohydride, NaBH Evaluation of the results by lighttransmission measurements indicated that small amounts of phenolica-ketone groups had been formed by the periodate reaction. Possibly 0.05a-hydroxypropioguiacone units or, more probably, 0.02-0.03 vanillinstructures had been created per orignal methoxyl unit.

The solubility of the demethylated products of Examples 1-8 wasdistinctly lower in the common lignin sol- OXIDATIVE DEMETHYLATION,USING $02 GAS AS THE REDUCTANT MATERIAL, OF ALKALI LIGNIN (OCHs content:14.16%)

Moles Product OCT-I3 Ex Demethylating agent NaIOr/ Liquid solvent Temp,Time, yield, content, No. moles C. min. percent percent OGHz,

2. 3 75% acetic acid 10 57 7. 52 2. 3 do 20 65 6. 99 2. 3 20 120 63 7.90 2. a 20 20 ss e. 13 9 2. 20 30 90 13. 72 20 30 95 14. 05 d0 20 30 9214. 19 7.3% acetic acid 0 2 a 68 7. 66 b 12 6. 84 1.0 80% acetic acid 022 92 8. 08 5 60% AcOH 20 10 72 6. 58

* First precipitate. b Second precipitate.

EXAMPLE 8 Alkali pine lignin, insoluble in water, (4.4 g.) Was'dissolvedin warm acetic acid (90%, 250 ml), the solution cooled to 2-3 C., and250 ml. of an ice-cooled solution of sodium metaperiodate (0.14 moles ofNaIO dissolved in 400 ml. of water and the solution made up to 1000 ml.with acetic acid) were added. After 3 minutes the reaction was stoppedby introducing a vigorous stream of S0 gas, while the reaction mixturewas cooled with icewater. After about 3 minutes, when the dark red colorof the reaction mixture, indicative of the formation of o-quinones, hadturned into a lighter shade, 500 ml. of water were added. Theprecipitate formed was centrifuged ofi, washed three times with smallamounts of water, and dried in vacuo over P 0 and NaOH. Yield was 3.0g., i.e., 68% (fraction 8a). While the washing procedure caused part ofthe material to peptize, another part remained dissolved in the motherliquor which still contained about acetic acid. The wash waters and themother liquor were combined and diluted with water to 2 liters; theprecipitate obtained was collected by centrifuging, washed twice with asmall amount of Water, and dried as above. Yield was 0.5 g., i.e., 12%(fraction 8b).

As shown by the methoxyl contents of the principal reaction products inTable 1, such as (8a), about of the original amount of OCH had beenremoved. It was thought possible that the residual fraction of thereaction products (30-35% of the alkali lignin used), which were highlysoluble in the dilute aqueous acetic acid mother liquors and thereforewere not recovered, had considerably lower methoxyl contents, but themethoxyl content of the secondarily-recovered product (8b) was reducedonly a 6.84%, i.e., 48% of the original methoxyl as compared to 54% for(8a).

The precipitate in 12% yield (8b), from the second dilution with water,had lost 54% of its original 001-1 groups. After methylation withdiazomethane, this material increased in methoxyl content from 6.84% OCHto 21.52%. Alkali lignin was similarly methylated. After comparison ofthe results, it was concluded that the majority of the groups formed onoxidative demethylation vents than that of untreated water-insolublealkali lignin. This loss in solubility seemed to indicate that somepolymerization of the primarily-formed o-quinoid elements had takenplace before the reduction with S0 was carried out. as discussedhereinbefore.

EXAMPLE 9 This reaction was completely successful in obtaining anunpolymerized product, apparently because of using the molar ration of1:1 for OCH :IO 8.8 grams of alkali lignin, containing 40Inilliequivalents of OCH groups, were dissolved in 500 ml. of aceticacid, cooled to a temperature between 0 C. and 2 C., and mixed rapidlywith 285 ml. of 0.14 molar NaIO solution, containing 40 milimoles ofiodate equivalent. After exactly 2.0 minutes reaction in which thesolution had become violet colored, S0 gas was introduced rapidly,turning the solution from violet to brown.

After reduction four liters of water were added to the solution,precipitating the reduced demethylated lignin. The precipitate wascentrifuged and washed with water three or four times. For the finalwashing, a single drop of perchloric acid was added to the wash water toovercome peptization properties of the lignin and promote dewatering ofthe lignin. The centrifuged, washed lignin was then'dried at 60 C. inair.

The yield was 8.1 grams or 92% of the original material. The product wasadded to dioxane; 5% did not dissolve and was removed by filtering. Thedioxane solution was added to ten times its volume of ether, and theprecipitate was centrifuged, washed twice with ether, and once withpetroleum ether, and dried. The reaction prod not, after precipitationwith water and recovering, was obtained in 92% yield, was completelysoluble in dioxane, and contained 8.65% OCH and 0.4% ash or 8.68% OCH onan ash-free basis.

EXAMPLE 10 Repeating the successful molar ratio of Example 9, thisexperiment used a 1:1 ratio of IO. ':OCH The reaction temperature wasraised to 20 C., and the reaction time was increased to 10 minutes. Theresulting yield, however, was only 72%, as given in Table 2, compared to92% for Example 9, but the methoxyl content was decreased to 6.58%.

In the analytical termination,

procedure of phenolic hydroxyl dedemethylation of alkali lignin didproceed i 3 merit. It could be stated that 80% of the 2,6-positions ofthe pyrocatechol nuclei had undergone substitution by CH OH groups.Another way of expressing the results is that each newly formed phenolichydroxyl group permitted almost two new methylol groups .to enter thedefurther than in these examples; typically, 65% of the methylatedlignin and that at least 80% of the 2,6-positotal amount of OCH wasrecovered as (ll-1 9E. The tions of the nuclei of kraft lignin are free,as the followdiscrepancy between the preparative experiments above inggeneral equation illustrates:

I r g he IOH CH o 26: AC; 3' I -l- & -"-il R OH CQ l R t Ci-l (1543 onand the typical analytical results is probably due to the fact wherein Rrepresents the substantially unaltered alkyl side that, as observed withother lignin preparations, part of chain of the original guaiacylpropane structure and R the guaiacyl residues are demethylatedcomparatively stands for a bond between the carbon atom of the phenylslowly and had not reacted during the short time intervals ring in theequation and the carbon atom of another phenyl used in these examples ascompared to the long time of group or of another propyl side chain.reaction (2-3 days) applied in the analytical procedure. Because alkalilignin, properly demethylated and re- EXAMPLES 11 14 duced, had the samereactivity with chlorocresol as the original alkali lignin, and further,because the aromatic ljour afldltlqnal exampigs are hsterd i b In @3911nuclei of untreated alkali lignin reacted with only 0.31 lhese eperlmemsi an amount OI alkah hgmn contam' moles of formaldeyhde, whereasthe demethylated lignin F 5 mllhequlvalents of H grollps w used reactedwith 0.95 moles of formaldehyde, calculated on the slum persulfate as analternative ox1dative' demethylat ng same basis, the increase inreactivity toward f0rma1de 5 hgher rfiacfiofl temperatufiis and longerhydetreatment could have been caused only by the higher tlmfas were,exglored m expeilments' After the aromatic reactivity of thedemethylated product. It was damn period m each the mlxture was f f withconcluded that the reactivity of kraft lignin in phenolgflsfious S02 andi diluted wlth,water' The hgnin formaldehyde condensation could beincreased significipitate was centrifuged, washed with water, and dried.camly by means of a carefully controlled demethylafion process. Table?The oxidative demethylation of alkali lignin in acetic gfiil i gg igigggagg acid with sodium metaperiodate is a very rapid reaction. It ismost suitably conducted in a continuous process, as Ill-Quid OCHS in apipeline reactor, in which the reductant, such as sul- Ei DemethylatingSolvent, Temp, Time not content, atur dioxide, may be added withinseconds after iodate agent (mmols) 1323,? o zli g percent addition,according to experimental determinations of optimum reaction time andoptimum reaction tempera- Kflszos (3,2) 70 181mmv 80 11.20 ture.Oxifdantive derl liethylation is irlijcreaksiedl1 by larger 12--IQSZOEQQ) Q 50 37 9.70 amountso t edemet ylative oxidant, ya ig. erreaction if M104 2O 20 76 1183 temperature, and by a longer reactiontime. The use 14-- K2S20s(5) 80 20 40 77 13-58 of over two moles ofsodium metaperiodate per mole 50 equivalent of methoxyl causes anexcessive amount of The demethylated product of Example 9 was condensedsecondary condensations to occur, giving undesirable with chlorocresolin presence of hydrochloric acid cataamounts of a polymerized, insolubleproduct and conlyst. The results indicated that 0.28 chlorocresol unitsper sequent loss of yield. OCH groups originally present in alkalilignin had been in a mildly-prepared lignin, such as Bjorkman ligninintroduced into the oxidatively demethylated lignin of this 55 which isnow considered to be very close to natural lignin invention, exactly thesame as for the original alkali lignin, in a structural sense, everythird guaiacyl propane buildindicating that the main structural featuresof the proing unit has a free phenolic OH group. The lignin of pane sidechains responsible for this condensation had not either coniferous ordeciduous woods when subjected to been altered by the oxidativedemethylation. alkali cooking undergoes certain different structural Thesame demethylated product was then methylolated 0 changes; from theviewpoint of this invention the most with formaldehyde and the resultantmaterial was further important consists of that part of theether-phenolic linkreacted with chlorocresol, producing a product thathad ages which are broken by cooking, producing alkali lignin 1.23chlorocresol units per OCH group present in the which has free phenolicgroups in about two-thirds of the original alkali lignin, indicatingthat 0.95 chlorocresol units building units. Because the method of thisinvention per original OCH had reacted with the methylol groups 5 worksonly with such building units having free phenolic introduced byformaldehyde after demethylation. Calhydroxyls, the economic advantagesare obvious for alkali culations showed that the oxidative demethylationprolignin as compared to natural lignin. cedure had resulted in theintroduction of 40 phenolic Afteroxidative demethylation of alkalilignin according hydroxyl groups, replacing a corresponding number of tothe methods of this invention, the propyl side chains methoxyl groupsout of each 100 OCH groups of alkali are unchanged, as demonstrated bythe chlorocresol exlignin. After methylolation, but not directly, thesenew per-iment described hereinbefore and by other evidence; phenolicgroups enabled 64 chlorocresol units to be linked furthermore,carbon-to-carbon bondings, between propyl to the nuclei, meaning thatevery newly-formed phenolic carbon atoms of two adjacent side chains,between a OH group had enabled 1.6 chlorocresol-reactive methylol propylcarbon and a carbon of a guaiacyl nucleus, or groups to be introducedafter alkaline formaldehyde treatbetween the carbons of two guaiacylnuclei, are not broken to a measurable extent. Even more significantly,for the 22% of the guaiacyl propane units having ether bonds at the No.4 position, the ether bonds in which an oxygen atom links the carbon ofa guaiaeyl nucleus to the carbon of a propyl side chain or to the carbonof another guaiacyl nucleus, are also not broken. In the oxidativedemethylation reaction of this invention, only a certain type of etherlinkage, termed a methoxyl group, in which oxygen joins the carbon of aguaiacyl nucleus to the carbon of a free methyl group, is attacked,provided that a phenolic hydroxyl group is in ortho position to themethoxyl group. The reaction of this invention, therefore, is specific.

Moreover, as demonstrated experimentally with Example No. 9hereinbefore, the reaction is easily controllable and technicallyuncomplicated. A. continuous process which includes the continuousregeneration of the iodate ion to the periodate ion by electrolyticoxidation is economically sound and can produce the reactive ligninproduct of this invention at a cost rendering it attractive as a usefulsubstituent in phenolic resins in the same manner as, and even moreusefully than, the original alkali lignin.

When the product of this invention is treated with formaldehyde, a largenumber of reactive benzyl alcohol groups, i.e., methylol groups, areintroduced into the guaiacyl nuclei than can be introduced into theguaiacyl nuclei of original or ordinary alkali lignin. These methylolgroups, by their inherent nature, as demonstrated hereinbefore withchlorocresol, can be condensed with phenols, cresols, etc., and providesubstitution sites for extending and reacting with phenolic materials toform thermoset-ting resins as is well known in the art.

Practical examples of lignin uses, and particularly of uses for a ligninof increased chemical reactivity, are, in the resin field:phenol-formaldehyde-lignins for molded products, as taught in No.2,357,090 and No. 2,282,518; lignin-containing coating compositions, astaught in No. 1,899,526 and No. 2,242,601; phenol-formaldehyde-ligninshell-molding resins, as taught in No. 2,751,650;phenolformaldehyde-lignin resin adhesives for lignocellulose productssuch as plywood, as taught in No. 2,878,197; andphenol-formaldehyde-lignin resoles for impregnating paper in themanufacture of laminates, :as taught in No. 2,683,706 and No. 2,725,321.Other uses may be illustrated with the elastomer field by No. 2,608,537for ligninrubber elastomers, No. 2,906,718 forlignin-rubber-polyisocyanate rubber, and No. 2,854,422 forlignin-diisocyanate elastomers.

We claim:

1. The method of oxidatively demethylating alkali lignin which comprisesreacting said lignin with an oxidizing agent, selected from the groupconsisting of sodium and potassium salts of bismuthate, periodate,persulfate, tungstenate, chlorite, hypochloride, hypobromide, andhypoidodide anions, chlorine dioxide with chlorine, hydrogen peroxide,and ozone, to convert guaiacol structures into o-quinoid structures,and, before the occurrence of a significant degree of polymerization bydiene addition of said quinoid structures, stopping the reaction with areducing agent selected from the group consisting of sulfur dioxide,sulfurous acid, sodium thiosulfate, and potassium thiosulfate, toconvert said o-quinoid structures into pyrocatechol structures.

2. The method of claim 1 wherein the lignin is dissolved in a solventwhich contains pro-tons and is inert to the oxidizing agent.

3. The method of claim 1 wherein the reduction is conducted in a solventwhich is a source of hydrogen.

4. The method of claim 1 wherein both oxidative demethylation andreduction are conducted in aqueous acetic acid.

5. The method of claim 1 wherein the oxidative demethylating reaction iscarried out at temperatures lower than ambient.

6. The method of claim 4 wherein the reaction occurs for a timeinversely proportioned to the temperature, a temperature of 0-4 C.corresponding to 2.0 minutes.

7. The method of increasing the aromatic reactivity of alkali lignincomprising the reacting of said lignin with up to 1.5 moles of sodiummetaperiodate per mole of methoxyl groups in the lignin and subsequentlyadding sulfur dioxide, said lignin being dissolved in a solvent inert tosodium metaperiodate, containing protons, and capable of supplyinghydrogen.

8. The method of claim 7 wherein the reaction is conducted attemperatures of 0-4 C.

9. The method of claim 7 wherein the reaction proceeds for up to 2.0minutes.

10. The method of increasing the aromatic reactivity of alkali lignin byreacting said lignin, dissolved in warm acetic acid at a ligninconcentration of 1 to 5% and cooled to 0 to 20 C., with sodiummetaperiodate at 0 to 20 C. for 1 to 3 minutes, employing up to 1.0moles of said periodate per 1.0 moles of methoxyl groups in the lignin,and reducing the reaction product with sulfur dioxide while cooling.

11. The method of preparing water'insoluble and substantiallyether-insoluble derivatives of alkali lignin having increased aromaticreactivity, as characterized by capacity to add larger proportions ofmethylol group by reaction with formaldehyde as compared to the originalalkali lignin, comprising oxidatively demethylating said lignin toconvert guaiacol structures into o-quinoid structures and, before theoccurrence of a significant degree of polymerization by diene additionof said quinoid structures, reducing said o-quinoid structures topyrocatcchol structures.

12. The method of claim 11 wherein the alkali lignin is oxidativelydemethyl-ated with an agent selected from the group consisting of thesodium and potassium salts of bismuthate, periodate, and tungstenate andwherein the o-quinoid structures are reduced to pyrocatechol structureswith an agent selected from the group consisting of sulfur dioxide,sulfurous acid, sodium thiosulfate, and potassium thiosulfate.

13. The product produced by the method of claim 11.

References Cited in the file of this patent UNITED STATES PATENTS2,669,592 MacGregor et a1 Feb. 16, 1954 FOREIGN PATENTS 1,213,766 FranceApr. 4, 1960 899,655 Germany Dec. 14, 1953 1,013,285 Germany Aug. 8,1957 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Noo 3071570 January 1 1963 Joseph Merton et a1,

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Coll unn i1 lines 55 and 56 for "hypochloride, hypobromide, andhypoldodlde" read hypochlorite hypobromite, and hypoiodite Signed andsealed this 10th day of September 1963a (SEAL) Attest:

DAVID L. LADD Commissioner of Patents ERNEST W. SWIDER Attesting Officer

1. THE METHOD OF OXIDATIVELY DEMETHYLATING ALKALI LIGNIN WHICH COMPRISESREACTING SAID LIGNIN WITH AN OXIDIZING AGENT, SELECTED FROM THE GROUPCONSISTING OF SODIUM AND POTASSIUM SALTS OF BISMUTHATE, PERIODATE,PERSULFATE, TUNGSTENATE, CHLORITE, HYPOCHLORIDE, HYPOBROMIDE, ANDDHYPOIDODIDE ANIONS CHLORINE DIOXIDE WITH CHLORINE, HYDROGEN PEROXIDE,AND OZONE, TO CONVERT GUAIACOL STRUCTURES INTO O-QUINOID STRUCTURES,AND, BEFORE THE OCCURRENCE OF A SIGNIFICANT DEGREE OF POLYMERIZATION BYDIENE ADDITION OF SAID QUINOID STRUCTURES, STOPPING THE REACTION WITH AREDUCING AGENT SELECTED FROM THE GROUP CONSISTING OF SULFUR DIOXIDE,SULFUROUS ACID, SODIUM THIOSULFATE, AND POTASSIUM THIOSULFATE, TOCONVERT SAID O-QUINOID STRUCTURES INTO PYROCATECHOL STRUCTURES.